1. Field of the Invention
The present invention relates to negative-working radiation-sensitive mixtures (e.g. those particularly useful as negative-working resist compositions) containing the admixture of a cyclized rubber polymer, a photoactive compound and an effective contrasting amount of at least one selected rubber-soluble azo dye containing a reactive acrylate or methacrylate group all dissolved in a solvent. Furthermore, the present invention also relates to substrates coated with these radiation-sensitive mixtures as well as the process of coating, imaging and developing these radiation-sensitive mixtures on these substrates.
2. Brief Description of the prior Art
Photoresist compositions are used in microlithographic processes for making miniaturized electronic components such as in the fabrication of integrated circuits and printed wiring board circuitry. In these processes, a thin coating or film of a photoresist composition is generally first applied to a substrate material, such as silicon wafers used for making integrated circuits or aluminum or copper plates of printed wiring boards. The preferred method of applying this film is spin coating. By this method, much of the solvent in the photoresist formulation is removed by the spinning operation. The coated substrate is then baked to evaporate any remaining solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure of radiation. This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam, ion beam, and X-ray radiant energy are radiation types commonly used today in microlithographic processes.
After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate. In some processes involving positive resists, it is desirable to bake the imaged resist coating before this developing step. This intermediate step is sometimes called post-exposure bake or PEB.
There are two types of photoresist compositions --negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g., a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to a developing solution. Thus, treatment of an exposed negative-working resist with a developer solution causes removal of the nonexposed areas of the resist coating and the creation of a negative image in the photoresist coating, and thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited but not exposed to the radiation. On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the resist composition exposed to the radiation become more soluble to the developer solution (e.g., the Wolff rearrangement reaction of the photoactive compound occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working resist with the developer solution causes removal of the exposed areas of the resist coating and the creation of a positive image in the photoresist coating. The desired portion of the underlying substrate surface is uncovered where the photoresist was exposed to the radiation.
Positive-working photoresist compositions are currently favored over negative-working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Yet negative-working resist are employed still in many specific applications.
One disadvantage with both conventional positive-working and negative-working resists is that they act as being transparent when coated on highly reflective substrates such as aluminum and other metals. This transparency property may lead to imprecise measurements of critical dimensions and pre-exposure alignments. With positive-working resists, it has been possible in the past to add one or more of a wide variety of nonactinic or contrast dyes to the resist composition. Contrast dyes enhance the visibility of the developed images and facilitate pattern alignment during manufacturing. Example of contrast dye additives which have been used in positive-working resists include Solvent Red 24 (C.I. No. 26105), Basic Fuchsin (C.I. 42514), Oil Blue N (C.I. No. 61555), and Calco Red A (C.I. No. 26125). However, the use of such known contrast dyes with negative-working resists having cyclized rubber as the binder polymer do not work because they rinse out of the negative-working resist during the wet development step with the commonly used negative resist organic developers such as liquid isoparaffinic hydrocarbon solutions or aromatic compounds such as xylene. Accordingly, there is a need for a contrast dye which can be incorporated in a negative-working resist having a cyclized rubber polymer, yet will not rinse out during the development step using a negative resist developer. The present invention is a solution to this need.